Return instead of forcibly exiting

This makes no difference currently as the script doesn't do anything
after this function finishes, but it allows any cleanup work to happen
at the end.

killstream/kill_stream.py

@@ -261,19 +261,19 @@ def terminate_long_pause(session_id, message, limit, interval, notify=None):
                 if state == 'paused':
                     if checked_time >= limit:
                         terminate_session(session_id, message, notify)
-                        sys.exit(0)
+                        return
                     else:
                         sleep(interval)
                 elif state == 'playing' or state == 'buffering':
                     sys.stdout.write(
                         "Session '{}' has resumed, ".format(session_id) +
                         "stopping monitoring.")
-                    sys.exit(0)
+                    return
         if not found_session:
             sys.stdout.write(
                 "Session '{}' is no longer active ".format(session_id) +
                 "on the server, stopping monitoring.")
-            sys.exit(0)
+            return
 
 
 if __name__ == "__main__":